PVC is a kind of general-thermoplastic with excellent performance and is one of the plastics with the largest output in China. PVC processing molding performance is poor. Accordingly, PVC must be filled with the processing modifying agent in order to improve its plasticization processing performance. Acrylate processing modifying agent is one of the best three kinds of the modifying agents which are adopted widely in China. But at present, the intrinsic viscosity coefficient of all acrylate processing modifying agents is usually less than 6.0. In general, when manufacturing acrylate plasticization modifying agent for PVC processing, the reaction temperature is usually higher than 65° C., and the raw material is added stepwise or batchwise to avoid intense reaction due to too much feed material or too high reaction temperature which damages the reactor and incurs danger. Now the intrinsic viscosity coefficients of PVC processing aids are all less than 7.0, and the processing performance of PVC modified is not ideal. In the prior art, there is no description about the relation between the intrinsic viscosity and PVC processing modifying agents.
In addition, regarding to the control of polymerization reaction, especially the polymerization reaction of acrylate plasticization modifying agents for PVC processing, almost all those skilled in the art believe that, because the reaction is an exothermal reaction, in order to prevent the excessive polymerization reaction, the reaction monomers must be added gradually or batchwise to the reactor, meanwhile maintain a relatively high reaction temperature in order to ensure the reaction to proceed smoothly. The polymerization reaction is hardly to occur under the lower reaction temperature.
The inventor filed patent application (No.200510079818.8) on Jun. 29, 2005, wherein a kind of plasticization modifying agent for PVC processing was disclosed. This modifying agent is a polymer obtained from the composition consisting of 0-100 parts by weight of alkyl methacrylate, 0-40 parts by weight of alkyl acrylate, 0-85 parts by weight of styrene monomers and 0-35 parts by weight of acrylonitrile monomers with total weight of 100 parts, the intrinsic viscosity of the polymer is higher than 7.5. The invention also provides the preparation method of this plasticization modifying agent for PVC processing. By the further experiments on this basis, the inventor found that the plasticization modifying agent with excellent performance can also be obtained under the conditions of different composition and preparation method from the above-mentioned application.